RE: MPE Question

["Anurag Sharma" <anurags@future.futsoft.com>]

Hi William,

DSM-CC doesn't carry any information about section packing.
The Payload Unit Start Indicator (PUSI) field in the MPEG header is used to
indicate the beginning of new DSM-CC section.
But that doesnt really specify if there is more than one section present in
the payload.
PSUI field in combination with other available information (DSM-CC headers)
can be used to check the presence of multiple sections in the payload.

Fragmentation of IP packets is supported, in case the size of the packet
exceeds a DSM-CC section size (4096 bytes)
In such cases section_number, last_section_number fields in the DSM-CC
header can be used for reassembly of the IP packets.

regards,
Anurag Sharma







-----Original Message-----
From: owner-ipdvb@erg.abdn.ac.uk [mailto:owner-ipdvb@erg.abdn.ac.uk]On
Behalf Of William StanisLaus
Sent: Friday, 29 April 2005 9:26 PM
To: ipdvb@erg.abdn.ac.uk
Subject: RE: MPE Question


Hi Siva and Bernhard,
DSM-CC which is a potential MPE of our present day DOES NOT support section
packing for normal IP data transmissions. In DSM-CC we have section length
of 12 bits, which can hold maximum of 4096 Bytes of payload data (IP in our
discussion). In Normal scenario we don't even use this big, since section
packing is not supported practically (theoretically YES), we use DVB router
one interface as Ethernet and other as DVB, on Ethernet wire we get only
1500 bytes the max, though there is a room for section
packing(theoretically) real time packet routing don't wait for another IP
packet, just push each and every ip packet received with MPE (DSM-CC) and to
MPEG2-TS (supports section packing, based on the timer - reason MPEG2-TS
MUST be 188 bytes, instead of wasting bytes with stuffing we have section
packing).

When we are talking about stuffing bytes, that was perfect by Bernhard, we
use for packet alignment, to be more specific, real time operating system
like PSOS, requires it be WORD aligned ( Multiples of Four) before
encryption algorithm to be applied for scrambling.

-William.

> -----Original Message-----
> From: owner-ipdvb@erg.abdn.ac.uk [mailto:owner-ipdvb@erg.abdn.ac.uk] On
> Behalf Of Bernhard Collini-Nocker
> Sent: Friday, April 29, 2005 6:55 AM
> To: ipdvb@erg.abdn.ac.uk
> Subject: Re: MPE Question
>
> Dear Siva,
>
> you are right in that I had understood your question different.
>
> Generally Sections do allow for numbering that is, one can put a payload
> (for example a DSM-CC object) into a number of Sections and with
> section_number and last_section_number the reassebler knows what to do.
> MPE uses this Section mechanism, so multiple Section operations should
> be possible. Actually I have never tested whether MPE decapsulators do
> support this in real, in principle they should (again the DVB
> databroadacst standard does not say too much, if anything, about it) but
> in DSM-CC Obejct carousels is a very usual mode of operation.
>
> Siva Veerepalli wrote:
> > Thanks for the response Bernhard, but I am a bit
> > confused about the answer. Please see my question
> > below:
> >
> > --- Bernhard Collini-Nocker <bnocker@cosy.sbg.ac.at>
> > wrote:
> >
> >>Siva Veerepalli wrote:
> [...]
> > I understand that two MPE sections could probably
> > start in the same TS packet (I guess that is what you
> > mean by section packing).
>
> Yes.
>
> > My original questions was, what is the usual practice
> > with regards to fragmenting an IP datagram over
> > multiple MPE sections (irrespective of how these
> > sections are transported in TS packets)? The DVB-H
> > (data broadcast standard) allows for this, however,
> > the IPDC interim specification requires that one
> > datagram be encapsulated entirely in one mpe section
> > i.e., no datagram fragmentation over multiple MPE
> > sections.
>
> Now the confusion starts when one introduces the wording of "over
> multiple MPE sections", because there is no such thing as a MPE section
> fragmentation.
> I will have to read the DVB-H standard again in order to find out what
> it really says. I guess the only real issues the DVB-H wrt to IP is
> addressing is the necessity of a IP datagram encapsulated in MPE is to
> support time slicing (ie a burst transmission of the resulting TS
> packets to allow for power saving) and MPE-FEC (adding redundant code to
> allow for reconstruction). In that case I woould assume that it is very
> reasonable (especially with legacy equipment) to avoid all potential
> interpretations of MPE wrt multiple section operation and section packing.
>
> > thanks,
> > Siva
> [...]
>
> Yor are very welcome,
> and I hope I got THE expected answer closer,
> Bernhard





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